Gasification is a high-temperature process usually conducted at elevated pressure that converts any carbon-containing material into a gas containing primarily carbon monoxide and hydrogen. Since this gas is often used for the synthesis of chemicals or synthetic hydrocarbon fuels, the gas is commonly known as “synthesis gas” or simply “syngas.” Gasification adds value to low- or negative-value feeds by converting them to marketable products. Typical feeds to gasification include coal; petroleum-based materials such as crude oil, coke, and high-sulfur residues; gases; and various waste materials.
The three basic types of gasifiers are: fixed bed, fluidized bed and entrained flow. A fixed bed gasifier operates at relatively low temperature (425° C.-600° C.) and requires a lower amount of oxygen compared to the other two types of gasifiers; however, the process produces synthesis gas containing methane, tars and oils. The fluidized bed gasifier operates at moderate temperature (900° C.-1050° C.) and requires more oxygen. An entrained flow gasifier operates at much higher temperature (1250° C.-1600° C.) and requires significantly higher energy input, but the carbon conversion is greater compared to fixed bed and fluidized bed types.
In addition to a source of electricity and fuel, syngas can be used for a wide range of products. Largely due to its hydrogen and carbon content, syngas can be a valuable source for producing chemicals, fertilizers, and industrial gases. A typical hydrogen to carbon monoxide ratio (H2:CO) of syngas is about 1:1 or less.
Certain products derived from syngas, including Fischer-Tropsch liquids, ammonia, hydrogen gas, urea, fuel gas, etc., each requires different and varying amounts of hydrogen and carbon monoxide. In some cases, chemical manufacturers can change products by adjusting the hydrogen and carbon monoxide contents of the syngas feed. In the case of using syngas as a fuel, the hydrogen to carbon monoxide ratio of the syngas often needs to be adjusted to meet various, and often changing, governmental restrictions on carbon dioxide emissions, typically per megawatt (MW) of power that is exported.
A need, therefore, exists for a process to adjust efficiently the hydrogen content of syngas to efficiently produce fuel and/or chemical products. There is also a need for efficiently varying production from one finished product to another with minimal downtime and capital costs.
The present embodiments are detailed below with reference to the listed Figures.